Let me explain why fuel consumption gets so bad in cars. Firstly it comes down to how you drive the car, if your going to drive the car at full revs all the time, take off from the lights fast, stop quickly at the lights and basically race around, your fuel consumption is going to suffer. There are a few other elements that comes into it as well, and that really is how you maintain your car. Proper maintenance of your car means the fuel system works to its optimum, this means the fuel can flow through the system smoothly, and you only use the fuel you need to get the car to work properly.
So watch how you drive the car, and make sure you have your fuel system service regularly, this will save you a lot of money in the long run.